There are known compressors which include a rotor that is provided in a gas turbine or the like and rotates around an axis, and a casing that encircles the rotor from an outer peripheral side and which compresses fluids, such as air. An air bleed structure for leading a portion of the compressed fluid to the outside is used for the compressors.
PTL 1 discloses an air bleed structure in which the shape of the section of a communication flow path (bleed passage) provided between a bleed slot and an air bleed chamber (bleed cavity) in the air bleed structure is changed to match the arrangement or shape of an air bleed tube (bleed port) in a peripheral direction.
In the air bleed structure, the arrangement of the above-described air bleed tube and the bled fluid have a swirling component in the peripheral direction accompanied with the rotation of the rotor. Thus, the flow rate of the fluid increases at the position in the peripheral direction of the communication flow path corresponding to the position where the air bleed tube is provided. When the flow rate of this fluid increases, it is confirmed from analysis using Computational Fluid Dynamics (CFD) that the non-uniformity of the flow rate distribution in the peripheral direction becomes large within the primary duct.
Depending on such nonuniform flow rate distribution, pulsation occurs, speed loss occurs in the vicinity of the tips of compressor blades arranged downstream from a bleed slot, and surging is caused in the entire flow of the compressed air.
The operation efficiency of the compressor may decline due to such speed loss and surging.
Particularly, when the number of air bleed tubes decreases from the purpose of weight reduction, or the like, the nonuniformity of the flow rate becomes larger and a surge margin becomes smaller. As a result, the possibility of the occurrence of the surging becomes higher.